1. Field of the Invention
This disclosure relates to improving battery life and adding larger capacity into existing high power battery system, wherein a battery management system and DC/DC converter and controller are added to control the energy release rate into power consumption device, such as hybrid and electric vehicle, from the secondary battery modules, thereby creating heterogeneous high power battery system.
2. Description of Related Art
Over the past few years, as global warming is becoming a major concern for the community and fossil fuel output is declining, there are active developments of electric vehicles and hybrid electric vehicles, which use high power battery modules that are over 1000 Watt-hour. The high power battery module is a major power source for an electric vehicle and is assistant power source for hybrid electric vehicles. A battery module usually consists of multiple packs or cells of battery with a battery management system. A battery management system monitors the voltage, current and estimates State Of Charge (SOC) of the battery module.
Majority of the high power batteries utilized in electric vehicles and hybrid vehicles are lead-acid and nickel-metal hydrate batteries. These batteries have very limited life cycle if the charging and discharging at unexpected high current rate in deep cycling. Like Toyota Prius(c) vehicle, the battery state of charge is maintained at 40% to 80% range in order to have a long design service life (100,000 miles to 150,000 miles). That means 60% of the battery capacity is not utilized during daily driving.
Some new battery chemistry, like Lithium cobalt oxide, Lithium iron phosphate, Lithium manganese oxide, has promising higher life cycles under control environment, lighter weight and higher energy density. However it also suffers from shorten life if discharged at high current rate and over-charged. And it is less durable as lead-acid and nickel-metal hydrate batteries under frustrating current demand during a vehicle transient from one speed to the other.
Currently, one common way to convert hybrid electric vehicle into higher energy storage plug-in hybrid electric vehicles is adding a new string of battery module directly to the stock battery module in parallel with relay control circuitry. It causes serious imbalance issues that reduce battery life because of different battery chemistry and different nominal voltage level. The combined battery modules can only charge and discharge at a limited SOC range set by the vehicle manufacturer. A significant portion of the capacity is not utilized as the result. There are some experimental techniques to ‘spoof’ OEM vehicle controller to force it to take advantage of the larger battery capacity. The side effect of doing that is higher cost and impacting the original manufacturer components and having higher emissions as designed since the original control algorithm is altered.
Another way to convert hybrid electric vehicle into plug-in hybrid electric vehicle is completely replacing the stock battery module with higher capacity one. This addresses battery imbalance issue but it is still has to limit the usable capacity in order to prolong battery life. And it is very expensive and causes environmental waste of the old battery module.
Wruck teaches dual battery system in U.S. Pat. No. 5,223,351, issued Jun. 29, 1993, titled Dual battery system. The problem with connecting two battery systems with different nominal voltage directly without isolation and converter control, is that the first battery with higher voltage will charge the second battery resulting in shifting of energy from the first battery to the second. As time goes on, two batteries are going to have the same voltage. It becomes a normal two parallel strings of battery packs.
In this disclosure, the primary goal is achieving longer battery life and higher capacity by managing multiple stage heterogeneous high power battery system with primary battery module handling transient load and secondary module(s) coping with constant load while have minimum impact to the primary battery module.